1. Field of the Invention
The invention relates to a device for winding and unwinding flat printed sheets onto or from a rotary winding drum. The winding drum has correlated therewith at least one winding belt for forming wound layers of printed sheets. The winding belt is removable from a winding mandrel and fed undershot to the winding drum. Means are provided for detecting the loading of the winding drum with regard to printed sheets.
2. Description of the Related Art
Devices of the aforementioned kind are well known in the printing industry as space-saving and inexpensive means for winding and unwinding printed sheets of newspapers and magazines. The winding of printed sheets onto the winding drum serves inter alia for intermediate storage, for transport and/or further processing of the printed sheets in an overlapped arrangement.
Prior art references disclosing such devices are CH 682 657 A5, EP 0 739 838 A2 as well as EP 0 826 616 A1 owned by the assignee.
For controlling the paper supply, it is required that during unwinding of the winding drum the empty state is reliably detected in a timely fashion. When the empty state is not recognized in a timely fashion, there is the risk that the winding belt is torn off. In the prior art, the recognition of the empty state is realized by optically or electrically detectable belt markings which are provided on the winding belt. An electrically detectable belt marking is, for example, a metal plate which is glued onto the winding belt or is otherwise fastened thereto. Such belt markings, however, can become ineffective during use by soiling or by being damaged. In order to prevent this, the winding belts must be checked and, if needed, replaced. Moreover, for recognizing belt markings it is often necessary to wind the winding belt back and forth which results in a considerable prolongation of the cycle time.
It is an object of the present invention to provide a device of the aforementioned kind which ensures a reliable but still inexpensive detection of loading of a winding drum.
In accordance with the present invention, this is achieved in that the means for detection comprise a touch probe which cooperates with the winding belt or the printed sheets and indicates whether the winding drum is empty or loaded.
In the device according to the invention, the touch probe is arranged on the winding drum and is thus not a component of the winding belt. The attachment of the touch probe on the winding drum is considerably simpler and less damage-prone than the attachment of a belt marking on the winding belt which belt is comparatively narrow and made of plastic material.
The touch probe can be realized in an especially simple way by a lever which can be supported in a springy fashion in a cutout at the periphery of the winding drum.
Preferably, this lever has, at a spacing to its pivot axle, a nose which projects, when the winding drum is empty, past the mantle surface of the winding drum and, when the winding drum is loaded, is moved radially inwardly by the winding belt or by the printed sheets against a restoring force of the spring.
When the winding drum is empty, the nose of the touch probe thus projects radially outwardly, while, when the winding drum is covered or loaded with printed sheets, this nose is pressed radially inwardly. The lever can thus have two positions wherein one position indicates the empty state and the other position the loaded state.
These two positions are detected in an advantageous manner according to a further development of the invention by means of a photocell. The detection is realized preferably by a light beam which impinges axis-parallel into the winding drum.
According to a further embodiment of the invention, the touch probe is arranged in the circumferential direction of the winding drum at a comparatively short spacing before the leading end of the winding belt. The empty state is already indicated when there is still a residual length of winding belt, respectively, of the winding layer present. The winding drum is thus still partially surrounded, for example, over half its circumference by the winding belt or the printed sheets. The unwinding process can thus be interrupted reliably and in a timely fashion. This ensures that the winding belt is not torn off the winding drum. During winding onto the winding drum, the loaded state is indicated as soon as the winding belt or the printed sheets applied in an overlapped arrangement have reached the touch probe.